This proposal undertakes the first systematic motion analyses of the performance of subjects with Parkinson's Disease (PD) in executing unconstrained, multi-joint 3D reaching movements. The focus is on uncovering the role that the basal ganglia may play in integrating sensory information from different sources into the motor plan. Three-dimensional pointing errors, movement kinematics, and interjoint coordination will be analyzed. Experiments utilize a programmable robot arm to present targets in known locations in one of two planes in space. Subjects will perform movements under a range of conditions which vary the available sensory information, memory demands, and task constraints. Spatial Perception Thresholds. Pure perceptual errors will be measured by having subjects' visually discriminate actual target locations from nearby locations presented 1-2 sec earlier and then extinguished. Pointing to Visually Defined Actual and Memorized Targets With and Without Vision of the Moving Arm. Disturbances in pointing movements to targets performed in darkened room will be investigated under different conditions of visual feedback: no visual feedback during the movement; vision of the moving fingertip but not of the target; vision of the target but not of the finger; vision of the fingertip and the target. Pointing to Memorized Targets Defined Proprioceptively. Two modes of proprioceptive target presentation will be used that will allow or prevent the subject from having access to central control signals underlying the arm movement. Pointing to Memorized Targets Defined Cutaneously. Disturbances in pointing movements to somatosensory targets also will be analyzed and compared to disturbances for visually or proprioceptively presented targets. Movement Speed Regulation: Peripheral Deficits versus Central Strategy Adaptation. Movements to memorize targets performed at different speeds with and without vision of the arm will be compared. Comparison Across Patient Groups. Finally, data on Parkinsonian subjects will be compared with separate data acquired on subjects lacking proprioceptive information from their limbs as well as subjects with unilateral cortical lesions. This combination of movement analyses with behavioral manipulations allows characterization of deficient motor performance and the ability to dissect out those elements of sensorimotor processing which may be most impaired in Parkinsonism.